Synthesis Of Aromatic Polyamides Containing Benzimidazole Structure And Their Wet Spinning Process

Poly(p-phenylene terephthalamide),known as aramid fiber 1414 in China,is one of high-tech synthetic fibers with the excellent properties such as high strength,high modulus,excellent thermal stability,low density and chemical resistance,so it is widely used in aerospace,composite materials,special clothing,electronic equipment and other fields.PPTA exhibits the ordered molecular structure,strong intermolecular hydrogen bonding and easy to be crystallized,so it does not melt even up to the decomposition temperature,and dose not dissolve in organic solvent,exclusive of concentrated sulfuric acid.The concentrated sulfuric acid used as solvent,meets a lot of difficult,such as the corrosion of equipment and equipment protect.By introducing a third monomer into the macromolecular chain is an efficient method to improve the solubility of PPTA and the cololymer may be spun by wet spinning.In this paper,the third monomer,2-(4-aminophenyl)-5-amino benzimidazole(DAPBI)was introduced in the low-temperature polycondensation of p-phenylene diamine(PPD)and terephthaloyl chloride(TPC)in NMP/Li Cl.A series of modified PPTA resins were obtained.The effects of the third monomer content,monomer molar concentration,initial reaction temperature,concentration of pyridine and Li Cl,the molar ratio,the reaction time and sequential structure on the intrinsic viscosity of the modified PPTA were discussed.The optimal polymerization conditions were as follows:the third monomer content was 43mol%,the monomer molar concentration was 0.2mol/L,initial reaction temperature was-5?,the amount of pyridine and the mass fraction of Li Cl were 2%and 4%,respectively,the molar ratiod is 1:1.01,and the reaction time was 15-20min.The structure of PPTA and the copolymers were characterized by Fourier transform infrared spectroscopy,and the results showed that the third monomer DAPBI was successfully introduced in PPTA.The crystalline performance of the polymers were analysed by X-ray diffraction,and the results showed that due to the addition of DAPBI,the tacticity of PPTA copolymers was destoried,the degree of crystallinity reduced significantly,and the tacticity of regular aromatic polyamide is better than that of random aromatic polyamide.Dissolution test showed that the solubility of PPTA was improved when DAPBI was added and the solubility of random aromatic polyamide was the best.With the increase of DAPBI content,the tensile strength and modulus of aromatic polyamide were promoted,and the elongation increased.The mechanical properties of regular aromatic polyamide have better mechanical properties than that of the random aromatic polyamide.When DAPBI was added,the thermal properties of aromatic polyamide reduced slightly but remained at a high level.The thermal properties of regular aromatic polyamide were better than that of random aromatic polyamide.With the increase of heterocyclic structures,the initial decomposition temperature of regular aromatic polyamide gradually increased,and the weight loss rate decreased gradually.When the content of the third monomer was 28 mol%,the copolymer solution cannot be spun due to the formation of gels and poor rhological behavior.When the content of the third monomer was more than 28 mol%,the polymerization system became a concentrated solution with the good spinnablity.With the increase of draft ratio of spinneret,both linear density and elongation decreased gradually,while tensile strength increased gradually,and at the same time fuzziness and broken wire appeared.According to the actual process operation and data comparison,the optimal conditions for the composition of the coagulation bath is NMP:H₂O=20:80,and the optimum coagulation bath temperature is 40?.With the increase of draft ratio of hot bath,both the fineness and the elongation at break decreased,the tensile strength has been greatly improved,and the fiber orientation increased.The increase of content of the third monomer results in a trend that the tensile strength increased first and then decreased,and the elongation at breat gradually increased.With the increase of heterocyclic segments in regular aromatic polyamide fiber,both the tensile strength and the elongation at break gradually increased.The mechanical property of regular aromatic polyamide fiber was generally higher than that of the random aromatic polyamide fiber...